a) Field of the Invention
This invention relates to a coating formulation of a hydrophobizing agent, said coating formulation being useful for a printing plate precursor enabling inscription of an image at a high speed and permitting regeneration for reuse, the printing plate precursor reusable by regeneration, a printing press allowing platemaking thereon, a fabrication process of a printing plate, and a regeneration process of the printing plate.
b) Description of the Related Art
In various printing processes, digitization of printing step is increasingly adopted in recent years. This digitization means to digitize data of an image or manuscript (hereinafter collectively called an “image”) by preparing the image with a personal computer or reading the image with a scanner or the like, and then to fabricate a printing plate directly from the digital data. This makes it possible to save the overall labor in the printing processes and also to conduct high-precision printing with ease.
As printing plates, so-called PS plates (presensitized plates) have been commonly used to date. A PS plate uses anodized aluminum as a hydrophilic non-image area, and has one or more hydrophobic image area formed on a surface of the anodized aluminum by curing a photosensitive resin. Fabrication of a printing plate with such a PS plate requires plural steps and hence, is time-consuming and costly. It is, therefore, the current situation that reductions in the time of printing process and in printing cost can hardly be promoted. Especially in small volume printing, the requirement for the plural steps is a cause of an increase in printing cost. Further, use of a PS plate requires a developing step which relies upon a developer. This developing step has raised a serious problem not only because of the need for a lot of time but also from the viewpoint of prevention of an environmental contamination upon treatment of a developer waste.
Further, it is a common practice for a PS plate to perform its exposure with a film, through which an original image is perforated, maintained in close contact with the presensitized surface of the PS plate. The fabrication of a printing plate has, therefore, become a problem in fabricating the printing plate directly from digital data and promoting digitization of the printing process. Moreover, after completion of printing of a pattern, it is necessary to replace the printing plate and then to conduct printing of a next pattern. Used printing plates have been thrown away.
To solve the above-described problems of PC plates, processes have been proposed to meet the digitization of printing processes while making it possible to omit the developing step, and some of such processes have come into commercial use. For example, JP-A-63102936 discloses a platemaking process which comprises using an ink, which contains a photosensitive resin, as an ink for a liquid ink-jet printer, injecting the ink against a printing plate precursor, and then irradiating light to cure an image area. JP-A-11254633, on the other hand, discloses a process for fabricating a color offset printing plate by an ink-jet head through which a solid ink is jetted.
Also included in known processes are a process for fabricating a printing plate, which comprises inscribing with a laser beam an image on a printing plate precursor—which is composed of a PET (polyethylene terephthalate) film, a laser absorbing layer such as carbon black arranged on the PET film and a silicone resin layer coated on the laser absorbing layer—to cause the laser absorbing layer to evolve heat and ablating off the silicone resin layer with the heat; and a process for fabricating a printing plate, which comprises coating a hydrophobic laser absorbing layer on an aluminum plate, coating a hydrophilic layer on the laser absorbing layer, and then ablating off the hydrophilic layer with a laser beam as in the above-described process.
In addition, a process has also been proposed for the fabrication of a printing plate, which comprises using a hydrophilic polymer as a printing plate precursor and exposing the hydrophilic polymer imagewise such that the hydrophilic polymer is cured at exposed areas.
However, unless replaced by a new printing plate subsequent to completion of printing of a pattern, the above-mentioned processes do not permit a next printing operation and hence, are not different from the conventional art in that a printing plate is thrown away after its use, although they can fabricate printing plates directly from digital data.
Also disclosed, for example, in JP-A-10250027 are a latent image block copy making use of a titanium oxide photocatalyst, a fabrication process of the latent image block, and a printing press having the latent image block. JP-A-11147360 also discloses an offset printing process by a printing plate making use of a photocatalyst.
Each of these techniques employs photocatalyst-activating light (practically, an ultraviolet ray) for the inscription of an image, and subjects a photocatalyst to heat treatment to regenerate a printing plate. Further, JP-A-11105234 discloses a fabrication process of a lithographic printing plate, which comprises hydrophilizing a photocatalyst with activating light, specifically an ultraviolet ray and then inscribing an image area by a heat-mode recording.
According to the paper (pages 124–125) entitled “Study on Behavior of Photoinduced Hydrophilization Associated with Structural Change in Titanium Oxide Surface (by Sanbe et al.) distributed at the Fifth Symposium on “Recent Developments of Photocatalytic Reactions” of the Photo Functionalized Materials Society in 1998, however, it is disclosed that hydrophilization of a titanium oxide photocatalyst by heat treatment was confirmed by Prof. Fujishima, Prof. Hashimoto, et al. of Research Center for Advanced Science and Technology, The University of Tokyo. By the processes disclosed in the laid-open patent applications referred to in the above, that is, the processes each of which hydrophobizes a photocatalyst by heat treatment to regenerate a printing plate, it is impossible to regenerate and reuse a printing plate or to fabricate a printing plate.
With the above-described circumstances in view, the present inventors already proposed printing plate precursors—each of which can fabricate a printing plate directly from digital data, can provide an image of practically sufficient quality without needing a developing step, that is, a developer, and can be regenerated for repeated use—and printing systems making use of the printing plate precursors. In the invention disclosed in JP-A-2000-062335, for example, a printing plate precursor with a titanium oxide catalyst contained on a surface thereof is used. A hydrophilic image area composed of an organic compound or the like is formed on the surface of the printing plate precursor, and together with a hydrophilic non-image area, forms a printed image. Subsequent to the printing, irradiation of activating light such as an ultraviolet ray makes it possible to decompose and remove the image area and also to hydrophilize the surface of the printing plate precursor, both, under action of the titanium oxide photocatalyst.
As a shortcoming, however, it is time consuming to achieve substantially complete decomposition and removal of the image area, specifically the organic compound or the like only by the photocatalyst on the surface of the printing plate precursor. Especially when a high molecular compound such as ink remains in the form of a thin layer on the surface of the printing plate precursor or in a like case, a lot of time is required for the decomposition and removal, and as a result, high-quality printing cannot be performed promptly.
With a view to shortening the time required to inscribe an image on a printing plate precursor and the time required to regenerate a printing plate and improving the resolution of the image, the present inventors have proceeded with further extensive research, leading to the completion of the present invention.
The present invention has been completed in view of the above-described circumstances, and has as an object thereof the provision of a coating formulation for a printing plate precursor, a printing plate precursor, a printing press, a fabrication process of a printing plate and a regeneration process of the printing plate, which make it possible to fabricate a printing plate directly from digital data, to obtain an image of practically sufficient quality without needing a developing step, that is, a developer, to regenerate and repeatedly use the printing plate precursor and also to speed up the processing-regeneration cycle of the printing plate precursor.